обработать список истории команд (process the command history list)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
fc — process the command history list
Синопсис (Synopsis)
fc [-r] [-e editor] [first [last]]
fc -l [-nr] [first [last]]
fc -s [old=new] [first]
Описание (Description)
The fc utility shall list, or shall edit and re-execute, commands
previously entered to an interactive sh.
The command history list shall reference commands by number. The
first number in the list is selected arbitrarily. The
relationship of a number to its command shall not change except
when the user logs in and no other process is accessing the list,
at which time the system may reset the numbering to start the
oldest retained command at another number (usually 1). When the
number reaches an implementation-defined upper limit, which shall
be no smaller than the value in HISTSIZE or 32767 (whichever is
greater), the shell may wrap the numbers, starting the next
command with a lower number (usually 1). However, despite this
optional wrapping of numbers, fc shall maintain the time-ordering
sequence of the commands. For example, if four commands in
sequence are given the numbers 32766, 32767, 1 (wrapped), and 2
as they are executed, command 32767 is considered the command
previous to 1, even though its number is higher.
When commands are edited (when the -l option is not specified),
the resulting lines shall be entered at the end of the history
list and then re-executed by sh. The fc command that caused the
editing shall not be entered into the history list. If the editor
returns a non-zero exit status, this shall suppress the entry
into the history list and the command re-execution. Any command
line variable assignments or redirection operators used with fc
shall affect both the fc command itself as well as the command
that results; for example:
fc -s -- -1 2>/dev/null
reinvokes the previous command, suppressing standard error for
both fc and the previous command.
Параметры (Options)
The fc utility shall conform to the Base Definitions volume of
POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
-e editor Use the editor named by editor to edit the commands.
The editor string is a utility name, subject to search
via the PATH variable (see the Base Definitions volume
of POSIX.1‐2017, Chapter 8, Environment Variables).
The value in the FCEDIT variable shall be used as a
default when -e is not specified. If FCEDIT is null or
unset, ed shall be used as the editor.
-l (The letter ell.) List the commands rather than
invoking an editor on them. The commands shall be
written in the sequence indicated by the first and last
operands, as affected by -r, with each command preceded
by the command number.
-n Suppress command numbers when listing with -l.
-r Reverse the order of the commands listed (with -l) or
edited (with neither -l nor -s).
-s Re-execute the command without invoking an editor.
Операнды (Operands)
The following operands shall be supported:
first, last
Select the commands to list or edit. The number of
previous commands that can be accessed shall be
determined by the value of the HISTSIZE variable. The
value of first or last or both shall be one of the
following:
[+]number A positive number representing a command
number; command numbers can be displayed with
the -l option.
-number A negative decimal number representing the
command that was executed number of commands
previously. For example, -1 is the
immediately previous command.
string A string indicating the most recently entered
command that begins with that string. If the
old=new operand is not also specified with
-s, the string form of the first operand
cannot contain an embedded <equals-sign>.
When the synopsis form with -s is used:
* If first is omitted, the previous command shall be
used.
For the synopsis forms without -s:
* If last is omitted, last shall default to the
previous command when -l is specified; otherwise,
it shall default to first.
* If first and last are both omitted, the previous 16
commands shall be listed or the previous single
command shall be edited (based on the -l option).
* If first and last are both present, all of the
commands from first to last shall be edited
(without -l) or listed (with -l). Editing multiple
commands shall be accomplished by presenting to the
editor all of the commands at one time, each
command starting on a new line. If first represents
a newer command than last, the commands shall be
listed or edited in reverse sequence, equivalent to
using -r. For example, the following commands on
the first line are equivalent to the corresponding
commands on the second:
fc -r 10 20 fc 30 40
fc 20 10 fc -r 40 30
* When a range of commands is used, it shall not be
an error to specify first or last values that are
not in the history list; fc shall substitute the
value representing the oldest or newest command in
the list, as appropriate. For example, if there are
only ten commands in the history list, numbered 1
to 10:
fc -l
fc 1 99
shall list and edit, respectively, all ten
commands.
old=new Replace the first occurrence of string old in the
commands to be re-executed by the string new.
Стандартный ввод (Stdin)
Not used.
Входные файлы (Input files)
None.
Переменные окружения (Environment variables)
The following environment variables shall affect the execution of
fc:
FCEDIT This variable, when expanded by the shell, shall
determine the default value for the -e editor option's
editor option-argument. If FCEDIT is null or unset, ed
shall be used as the editor.
HISTFILE Determine a pathname naming a command history file. If
the HISTFILE variable is not set, the shell may attempt
to access or create a file .sh_history in the directory
referred to by the HOME environment variable. If the
shell cannot obtain both read and write access to, or
create, the history file, it shall use an unspecified
mechanism that allows the history to operate properly.
(References to history ``file'' in this section shall
be understood to mean this unspecified mechanism in
such cases.) An implementation may choose to access
this variable only when initializing the history file;
this initialization shall occur when fc or sh first
attempt to retrieve entries from, or add entries to,
the file, as the result of commands issued by the user,
the file named by the ENV variable, or implementation-
defined system start-up files. In some historical
shells, the history file is initialized just after the
ENV file has been processed. Therefore, it is
implementation-defined whether changes made to HISTFILE
after the history file has been initialized are
effective. Implementations may choose to disable the
history list mechanism for users with appropriate
privileges who do not set HISTFILE; the specific
circumstances under which this occurs are
implementation-defined. If more than one instance of
the shell is using the same history file, it is
unspecified how updates to the history file from those
shells interact. As entries are deleted from the
history file, they shall be deleted oldest first. It is
unspecified when history file entries are physically
removed from the history file.
HISTSIZE Determine a decimal number representing the limit to
the number of previous commands that are accessible. If
this variable is unset, an unspecified default greater
than or equal to 128 shall be used. The maximum number
of commands in the history list is unspecified, but
shall be at least 128. An implementation may choose to
access this variable only when initializing the history
file, as described under HISTFILE. Therefore, it is
unspecified whether changes made to HISTSIZE after the
history file has been initialized are effective.
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base
Definitions volume of POSIX.1‐2017, Section 8.2,
Internationalization Variables for the precedence of
internationalization variables used to determine the
values of locale categories.)
LC_ALL If set to a non-empty string value, override the values
of all the other internationalization variables.
LC_CTYPE Determine the locale for the interpretation of
sequences of bytes of text data as characters (for
example, single-byte as opposed to multi-byte
characters in arguments and input files).
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
Асинхронные события (Asynchronous events)
Default.
Стандартный вывод (Stdout)
When the -l option is used to list commands, the format of each
command in the list shall be as follows:
"%d\t%s\n", <line number>, <command>
If both the -l and -n options are specified, the format of each
command shall be:
"\t%s\n", <command>
If the <command> consists of more than one line, the lines after
the first shall be displayed as:
"\t%s\n", <continued-command>
Стандартный вывод сообщений (Stderr)
The standard error shall be used only for diagnostic messages.
Выходные файлы (Output files)
None.
Расширенное описание (Extended description)
None.
Статус выхода (Exit)
The following exit values shall be returned:
0 Successful completion of the listing.
>0 An error occurred.
Otherwise, the exit status shall be that of the commands executed
by fc.
Последствия ошибок (Consequences of errors)
Default.
The following sections are informative.
Использование в приложениях (Application usage)
Since editors sometimes use file descriptors as integral parts of
their editing, redirecting their file descriptors as part of the
fc command can produce unexpected results. For example, if vi is
the FCEDIT editor, the command:
fc -s | more
does not work correctly on many systems.
Users on windowing systems may want to have separate history
files for each window by setting HISTFILE as follows:
HISTFILE=$HOME/.sh_hist$$
Примеры (Examples)
None.
Обоснование (Rationale)
This utility is based on the fc built-in of the KornShell.
An early proposal specified the -e option as [-e editor [old= new
]], which is not historical practice. Historical practice in fc
of either [-e editor] or [-e - [ old= new ]] is acceptable, but
not both together. To clarify this, a new option -s was
introduced replacing the [-e -]. This resolves the conflict and
makes fc conform to the Utility Syntax Guidelines.
HISTFILE Some implementations of the KornShell check for the
superuser and do not create a history file unless
HISTFILE is set. This is done primarily to avoid
creating unlinked files in the root file system when
logging in during single-user mode. HISTFILE must be
set for the superuser to have history.
HISTSIZE Needed to limit the size of history files. It is the
intent of the standard developers that when two shells
share the same history file, commands that are entered
in one shell shall be accessible by the other shell.
Because of the difficulties of synchronization over a
network, the exact nature of the interaction is
unspecified.
The initialization process for the history file can be dependent
on the system start-up files, in that they may contain commands
that effectively preempt the settings the user has for HISTFILE
and HISTSIZE. For example, function definition commands are
recorded in the history file. If the system administrator
includes function definitions in some system start-up file called
before the ENV file, the history file is initialized before the
user can influence its characteristics. In some historical
shells, the history file is initialized just after the ENV file
has been processed. Because of these situations, the text
requires the initialization process to be implementation-defined.
Consideration was given to omitting the fc utility in favor of
the command line editing feature in sh. For example, in vi
editing mode, typing "<ESC>v" is equivalent to:
EDITOR=vi fc
However, the fc utility allows the user the flexibility to edit
multiple commands simultaneously (such as fc 10 20) and to use
editors other than those supported by sh for command line
editing.
In the KornShell, the alias r (``re-do'') is preset to fc -e -
(equivalent to the POSIX fc -s). This is probably an easier
command name to remember than fc (``fix command''), but it does
not meet the Utility Syntax Guidelines. Renaming fc to hist or
redo was considered, but since this description closely matches
historical KornShell practice already, such a renaming was seen
as gratuitous. Users are free to create aliases whenever odd
historical names such as fc, awk, cat, grep, or yacc are
standardized by POSIX.
Command numbers have no ordering effects; they are like serial
numbers. The -r option and -number operand address the sequence
of command execution, regardless of serial numbers. So, for
example, if the command number wrapped back to 1 at some
arbitrary point, there would be no ambiguity associated with
traversing the wrap point. For example, if the command history
were:
32766: echo 1
32767: echo 2
1: echo 3
the number -2 refers to command 32767 because it is the second
previous command, regardless of serial number.
Будущие направления (Future directions)
None.
Смотри также (See also)
sh(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
